The present invention relates to automatic injection devices (“autoinjectors”). In particular, the present invention relates to an autoinjector having an automatically deployable frontal buttress.
Autoinjector mechanisms have commercially been developed to substitute an automated mechanism for the manual action of inserting a hypodermic needle into a recipient's flesh and forcing the liquid medicament out of the syringe, through the hypodermic needle and into the recipient. In some cases, the automated mechanisms are designed to utilize commercially commonplace pre-filled syringes. The pre-filled syringes are typically manufactured by pharmaceutical companies, or in some cases a third party. The manufacturers thereafter assemble the pre-filled syringes into autoinjectors for commercial distribution. Examples of such devices include the EpiPen® manufactured by Meridian Medical Technologies, Inc., of Bristol, Tenn., the Humira® manufactured by Owen Mumford Ltd., of Oxford, United Kingdom, and the SureClick® system marketed by Scandinavian Health Limited, of Florham Park, N.J. Autoinjectors have proven to be beneficial for patients exhibiting psychological paranoia of receiving parenteral injections (e.g., needle phobic individuals and young children) and/or those without the manual dexterity or clear eyesight necessary to self-administer injections using conventional syringes.
Conventional autoinjectors generally provide a compression spring-based mechanism to drive the syringe in the distal direction within a housing (the housing contains the syringe) and some means to initiate the automatic injection process. When triggered, the compressed spring is released from end-to-end confinement. Typically, the spring is confined to abut against an interior surface of the housing about its proximal end such that releasing the compressed spring causes axial extension in the distal direction. The spring, typically acting through one or more surrogate components, impinges upon the syringe, and/or an elastomeric piston element thereof, causing the syringe to translate in the distal direction until the hypodermic needle associated with the syringe extends beyond the distal end of the housing.
The extended length of the needle determines the depth of drug delivery at the injection site. The exposed length of the needle (i.e., that portion of the needle exterior to the autoinjector housing at needle extension) is known as the “needle insertion depth.” The correlation between extended length and insertion depth assumes that the distal end of the autoinjector is pressed against the injection site during autoinjector actuation. In most therapeutic applications, it is important that the depth of needle insertion be accurately controlled so as to assure the drug is delivered into a specific tissue mass, for example the subcutaneous tissue residing between the dermal skin layer and the musculature. Known and repeatable length of needle insertion is therefore a desirable attribute of autoinjector devices.
Billions of pre-filled syringes as described above are manufactured of borosilicate glass on an annual basis. The proximal end of the glass syringe is formed into a radially disposed, disk-shaped flange. The flange is thereafter cut on two sides in parallel planes in close proximity to the syringe body to form oblong and opposing finger grips. This glass syringe configuration is know as a cut-flange configuration. Glass syringes, and more particularly cut flange syringes, represent a number of challenges in autoinjector applications because they are fragile and easily broken components with a relatively high degree of dimensional variability. The high degree of dimensional variability leads to variability in the exposed length of the hypodermic needle beyond the distal end of the glass syringe and the overall length of the syringe. In addition, the cut flanges of such glass syringes have varying degrees of irregularity and asymmetry with respect to a central axis along the center of the syringe barrel and a plane perpendicular to the central axis.
Conventional autoinjectors are configured to stop the syringe at a desired forward position at the end of needle insertion based off of the syringe flange. That is, the syringe flange becomes a de facto point of registration, in other words a datum surface, which dictates the relative axial relationship between the syringe features and the other elements of the autoinjector. Under such configurations, any variability, whether associated with the overall length of the syringe, length of the exposed needle, or variability associated with the flange itself, translates directly into variability in the extended needle length and needle insertion length. In addition, due to the abrupt deceleration of the syringe/carrier assembly at the end of needle insertion, impact loads are imposed on the fragile syringe flanges. In other words, the force applied by the autoinjector in driving the syringe distally creates an opposing force imposed on the flange by its registration point of contact. In addition, a bending moment is borne by the flange as a result of the radial distance between the centerline of the piston and the flange. The bending moment increases the stress applied to the fragile flange increasing the risk of fracture.
Moreover, conventional autoinjectors are typically configured with a fixed stroke length. That is, conventional autoinjectors are designed to drive the plunger of the syringe a fixed distance from some fixed reference point on the autoinjector. Thus, with increased variability in the overall length of the glass syringe used in such autoinjectors, the fixed stroke length results in increased variability of residual medicament volume after injection. Such variability in residual medicament volume translates into significant monetary waste due to the relatively high cost of the drugs used to manufacture the medicaments.
Thus, conventional autoinjectors are deficient in that they cannot accommodate conventional pre-filled glass syringes (i.e., staked-needed syringes) to effectively address the issues associated with fragile and irregular components while assuring accurate needle placement and precise dose delivery due to the dimensional variability of glass syringe manufacturing. As such, there is still a need for an autoinjector that can provide accurate needle insertion depth and precise dose delivery.
In addition, conventional pre-filled glass syringes are typically supplied as an assembly with a needle shield that includes an elastomeric element to provide a means to sealably encapsulate the hypodermic needle. FIG. 2A illustrates a conventional pre-filled glass syringe 46 having a barrel 51. The needle shield 60 serves as a sterility barrier for the needle 61 (FIG. 2B) and its fluid contents as the syringe 46 is pre-sterilized at the factory. Once delivered to the pharmaceutical company, the pre-filled syringe is filled with medicament within a sterile filling suite. Often, the needle shield 60 is itself encapsulated with a rigid component to provide additional protection against needle damage and to provide a suitable means to manually remove the needle shield 60. Thus, the needle shield 60 is commonly know as a rigid needle shield (“RNS”). In such RNSs, an open end allows access to the elastomeric interior through which the needle 61 is introduced into the elastomeric interior. The RNS is removably attached to the syringe 46 by a circumferential compression fit between the compliant elastomeric element of the RNS and cooperative features present on the distal end of the syringe 46. In addition, such RNSs have an overall outer diameter that is approximately the same as that of the syringe 46.
Such conventional syringes 46 can be used as a stand alone manually operable syringe 46 or in combination with a suitable autoinjector. Such autoinjectors are provided with a means to remove the RNS before administering the injection. This is typically accomplished by a component provided as part of the autoinjector that engages the needle shield during final assembly and provides a graspable handle with which a user can grasp to extract the needle shield in the axial, distal direction. However, the use of such handles to disengage the RNS creates an annular void or open end about the distal end of the autoinjector. Moreover, as the handle to remove the RNS occupies space at the distal end on the autoinjector, this precludes the use of such space for any potential buttress surface upon which the syringe 46 may engage.
Consequently, an autoinjector that is capable of accommodating a glass, cut flange syringe with a RNS attached would present pharmaceutical companies with a significant advantage in being able to provide one primary pre-filled syringe that can be used either in a manual setting or, alternatively, in conjunction with an autoinjector.